Field of the Invention
This invention relates to a liner incorporated into a tubular passage of a semi-axial flow pump and, more particularly, to a liner which is most suitably used in a small-sized boat (hereinafter referred to simply as "Jet Ski" which is a registered trademark of the assignee of this application) which is equipped with a water jet type propulsion device using such a semi-axial flow pump.
Generally, in the water jet type propulsion device of a "Jet Ski" which uses a semi-axial flow pump b, as shown in FIG. 3, an impeller c of the pump b is mounted on a driving shaft a extended from a prime mover. A tubular passage d of the pump b has a truncated-conical passage portion e, inside which the impeller c is disposed. The semi-axial flow pump b is arranged such that it imparts pressure energy to a water sucked-in from a suction port f which is opened in that bottom portion of the boat at the position forwardly of the conical pipepassage portion e, said pressure energy in the water being converted into kinetic energy at a pump nozzle g, thereby the water is ejected outside the boat through a steering nozzle h, so that, with the reaction thus produced, a body of the boat is caused to advance or have its advancing direction altered. A vane guide i is connected to a boss k by means of radial stationary vanes j. The boss k interiorly supports the driving shaft a through a bearing l so that that shaft may rotate about its axis. The passage d in the prior art as well is a casting which consists of a light alloy, for purpose of anti-corrosive features and reduced weight. Since the "Jet Ski" equipped with the above-mentioned water jet type propulsion device has no projection from the outer surface of the boat bottom, it can be allowed to travel even in very shallow water. However, when the "Jet Ski" is allowed to travel in shallow water along the seashore, sands and the like are sucked into the suction port f together with water. This raised a problem that when these sands and the like pass through the pump b, they are radially accelerated and moved toward the inner periphery of the pipe passage d, by a centrifugal force, to remarkably wear the inner peripheral wall of the truncated conical pipe-passage portion e made of light alloy.